Lead positioning and finned fixation system

ABSTRACT

A therapy assembly configured for at least partial insertion in a living body. At least one fixation structure is attached to the therapy delivery element proximate the electrodes. The fixation structure is configured to collapse radially inward and wrap circumferentially around the therapy delivery element to a collapsed configuration when inserted into a lumen of an introducer. The fixation structures deploy to a deployed configuration when the introducer is retracted. The fixation structure includes major surfaces generally parallel with, and extending radially outward from, a central axis of the therapy delivery element, proximal edge surface oriented toward the proximal end, and a distal edge surface oriented toward the distal end. The proximal and distal edge surfaces provide generally symmetrical resistance to displacement of the therapy delivery element within the living body in either a proximal direction or a distal direction along the central axis.

PRIORITY DATA

This application is a continuation of U.S. patent application Ser. No.14/712,073, filed May 14, 2015, now U.S. Pat. No. 9,717,900 which is acontinuation of U.S. patent application Ser. No. 13/537,341, filed onJun. 29, 2012, which are incorporated by reference herein in theirentirety.

FIELD

The present disclosure is directed to a method and apparatus that allowsfor stimulation of body tissue, particularly nerves. More specifically,the implantable medical electrical lead includes at least one axiallyoriented fixation structure with leading and trailing edge surfaces toprovide generally symmetrical bi-axial fixation.

BACKGROUND

Implantable medical electronics devices consist of an implanted pulsegenerator that is used to provide electrical stimulation to certaintissues and an implantable lead or leads that are used to transmit theelectrical impulse to the targeted tissues. Examples include cardiacpacemaking, and a number of related applications for cardiac rhythmmanagement, treatments for congestive heart failure, and implanteddefibrillators. Other applications for implantable pulse generatorsinclude neurostimulation with a wide range of uses such as pain control,nervous tremor mitigation, incontinence treatment, epilepsy seizurereduction, vagus nerve stimulation for clinical depression, and thelike.

Despite various suture fixation devices, nerve stimulation leads can bedislodged from the most efficacious location due to stresses placed onthe lead by the ambulatory patient. A surgical intervention is thennecessary to reposition the electrode and affix the lead. Theimplantable pulse generator (“IPG”) is programmed to deliver stimulationpulse energy to the electrode providing the optimal nerve response. Theefficacy of the selected electrode can fade over time due todislodgement or other causes.

Physicians spend a great deal of time with the patient under a generalanesthetic placing the small size stimulation electrodes relative to thetarget nerves. The patient is thereby exposed to the additional dangersassociated with extended periods of time under a general anesthetic.Movement of the lead, whether over time from suture release or duringimplantation during suture sleeve installation, is to be avoided. As canbe appreciated, unintended movement of any object positioned proximate anerve may cause unintended nerve damage. Moreover reliable stimulationof a nerve requires consistent nerve response to the electricalstimulation that, in turn, requires consistent presence of thestimulation electrode proximate the target nerve. On the other hand, ifthe target nerve is too close to the electrode, inflammation or injuryto the nerve can result, diminishing efficacy and possibly causingpatient discomfort.

Cardiac pacing leads are commonly provided with passive fixationmechanisms that non-invasively engage heart tissue in a heart chamber orcardiac blood vessel or active fixation mechanisms that invasivelyextend into the myocardium from the endocardium or epicardium.Endocardial pacing leads having pliant tines that provide passivefixation within interstices of trabeculae in the right ventricle andatrial appendage are well known in the art as exemplified by U.S. Pat.Nos. 3,902,501, 3,939,843, 4,033,357, 4,236,529, 4,269,198, 4,301,815,4,402,328, 4,409,994, and 4,883,070. Such tined leads typically employtines that extend outwardly and proximally from a band proximal to adistal tip pace/sense electrode and that catch in natural trabecularinterstices when the distal tip electrode is advanced into the a trialappendage or the ventricular apex.

Certain spinal cord stimulation leads have been proposed employing tinesand/or vanes as stand-offs to urge the stimulation electrode in theepidural space toward the spinal cord as disclosed in U.S. Pat. Nos.4,590,949 and 4,658,535, for example, and to stabilize the stimulationelectrode in the epidural space as disclosed in U.S. Pat. No. 4,414,986,for example.

Stimulation leads for certain pelvic floor disorders have been proposedwith a fixation mechanism that includes a plurality of time elementsarrayed in a tine element array along a segment of the lead proximal tothe stimulation electrode array, such as for example in U.S. Pat. Nos.6,999,819; 7,330,764; 7,912,555; 8,000,805; and 8,036,756. Each tineelement includes a plurality of flexible, pliant, tines. The tines areconfigured to be folded inward against the lead body when fitted intoand constrained by the lumen of an introducer.

Peripheral nerve field stimulation (“PNFS”) involves delivery ofstimulation to a specific peripheral nerve via one or more electrodesimplanted proximate to or in contact with a peripheral nerve, such asdisclosed in U.S. Pat. Publication No. 2009/0281594. PNFS may be used todeliver stimulation to, for example, the vagal nerves, cranial nerves,trigeminal nerves, ulnar nerves, median nerves, radial nerves, tibialnerves, and the common peroneal nerves. When PNFS is delivered to treatpain, one or more electrodes are implanted proximate to or in contactwith a specific peripheral nerve that is responsible for the painsensation.

During the implantation procedure the surgeon selectively activates theelectrodes to test nerve response (also referred to as “mapping”) todetermine optimal lead position. Fixation structures on the lead aretypically restrained by the introducer during the mapping process.Optimal lead placement must be achieved before deploying any fixationstructures.

Prior art fixation strategies include barbed or angled structures thatprovide greater fixation in one direction along the central axis of thelead. For example, U.S. Pat. No. 7,684,873 (Gerber) and U.S. Pat. No.6,999,819 (Swoyer et al.) both disclose fixation tines angled withrespect to the central axis of the lead. This approach tends to provideexcess fixation in the proximal direction, complicating lead removal,and inadequate fixation in the distal direction.

The asymmetry in these fixation approaches creates greater risk of thelead being inadvertently displaced in the distal direction, such as bypatient movement, rather than in the proximal direction. For example, ifthe lead is subjected to cyclical push-pull forces, the angled tinesprovide a ratcheting-action that favors displacement in the distaldirection over the proximal direction. Over time, the lead will tend tomigrate in the distal direction, resulting in misplacement of theelectrodes relative to the target nerve tissue.

BRIEF SUMMARY

The present disclosure is directed to a therapy assembly configured forat least partial insertion in a living body. The therapy assemblyincludes a therapy delivery element with a proximal end having aplurality of electrical contacts configured to electrically couple withan implantable pulse generator, and a distal end with a plurality ofelectrodes that are electrically coupled to the electrical contacts atthe proximal end. An introducer with a lumen configured to receive thetherapy delivery element is provided. At least one fixation structure isattached to the therapy delivery element near the electrodes. Thefixation structure is configured to collapse radially inward and wrapcircumferentially around the therapy delivery element to a collapsedconfiguration when inserted into the lumen of the introducer. The atleast one fixation structure deploys to a deployed configuration whenthe introducer is retracted. The fixation structure includes majorsurfaces generally parallel with, and extending radially outward from, acentral axis of the therapy delivery element. The at least one fixationstructure also includes a proximal edge surface oriented toward theproximal end, and a distal edge surface oriented toward the distal end.The proximal and distal edge surfaces provide generally symmetricalresistance to displacement of the therapy delivery element within theliving body in either a proximal direction or a distal direction alongthe central axis.

In one embodiment, the at least one fixation structure includes aplurality of fixation structures that wrap circumferentially around thetherapy delivery element in a non-overlapping configuration wheninserted into the lumen of the introducer. A plurality of fixationassemblies can be axially spaced along the therapy delivery element. Thefixation assemblies preferably include a plurality of fixationstructures. In one embodiment, the fixation assemblies are rotationallyoffset so the proximal and distal edge surfaces of the fixationstructures on at least two fixation assemblies are out-of-plane. Theaxial spacing between the fixation assemblies is typically in a range ofbetween about 0.050 inches to about 0.150 inches.

The fixation structures preferably have a radial dimension in a rangebetween about 0.030 to about 0.150, and more preferably in a rangebetween about 0.045 inches to about 0.065 inches, and an axial dimensionin a range of about 0.050 inches to about 0.200 inches. A therapydelivery element with the present fixation structures exhibit apullout-force from the living body in a range of between about 0.50pounds to about 3.00 pounds.

The fixation structure can be bonded directly to the therapy deliveryelement or attached to a sleeve that is bonded to the therapy deliveryelement. The at least one fixation structure optionally includes atleast one edge surface oriented at an angle relative to a central axisof the therapy delivery element. The at least one fixation structure canbe rectangular, trapezoidal, circular, curvilinear, or triangular.

In one embodiment, the fixation structures include at least fourproximal edge surfaces and four distal edge surfaces. The proximal edgesurfaces preferably have a total surface area within about +/−20% orless than a total surface area of the distal edge surfaces. The fixationstructure provides a resistance to a displacement force applied to thetherapy delivery element in the proximal direction is within about+/−20% or less to resistance to a displacement force applied in thedistal direction.

The present disclosure is also directed to a method of implanting atherapy assembly in a living body. The method includes inserting anintroducer adjacent into the living body near an implantation site. Adistal end of a therapy delivery element is then inserted into a lumenin the introducer to collapse radially inward fixation structuresattached to the therapy delivery element near the distal end. Thetherapy delivery element is rotated slightly during insertion into theintroducer to wrap the fixation structures circumferentially around thetherapy delivery element to a collapsed configuration. Placement of thetherapy delivery element in the living body is confirmed. The introduceris retracted out of the living body to deploy the fixation structures toa deployed configuration. The fixation structures include major surfacesgenerally parallel with, and extending radially outward from a centralaxis of the therapy delivery element, a proximal edge surface orientedtoward the proximal end of the therapy delivery element, and a distaledge surface oriented toward the distal end of the therapy deliveryelement.

The method includes electrically coupling electrical contacts at aproximal end of the therapy delivery element with an implantable pulsegenerator. The method includes the step of engaging the proximal anddistal edge surfaces with tissue in the living body to provide generallysymmetrical resistance to displacement of the therapy delivery elementin either a proximal direction or a distal direction along the centralaxis.

In one embodiment, the method includes wrapping the fixation structurescircumferentially around the therapy delivery element in anon-overlapping configuration when in the collapsed configuration. Themethod optionally includes axially spacing a plurality of fixationassemblies along the therapy delivery element. The plurality of fixationassemblies on the therapy delivery element can be rotationally offset sothe proximal and distal edge surfaces of the fixation structures on atleast two fixation assemblies are out-of-plane. In one embodiment, theplurality of fixation structures on the therapy delivery element arearranged with at least four proximal edge surfaces and four distal edgesurfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a therapy delivery system.

FIG. 2A is a schematic illustration of an implantable pulse generatorand a therapy delivery element in accordance with an embodiment of thepresent disclosure.

FIG. 2B is a schematic illustration of a lead extension and a therapydelivery element in accordance with an embodiment of the presentdisclosure.

FIG. 3 is a schematic illustration of a therapy delivery system forspinal cord stimulation in accordance with an embodiment of the presentdisclosure.

FIG. 4 is an alternate illustration of an implantable pulse generatorwith a therapy delivery element in accordance with an embodiment of thepresent disclosure.

FIG. 5 is a schematic illustration of a therapy delivery system fortreating pelvic floor disorders in accordance with an embodiment of thepresent disclosure.

FIG. 6 is a schematic illustration of a therapy delivery system forperipheral nerve stimulation in accordance with an embodiment of thepresent disclosure.

FIG. 7A illustrates a therapy assembly in an introducer in accordancewith an embodiment of the present disclosure.

FIG. 7B illustrates the introducer of FIG. 7A retracted to expose theelectrodes in accordance with an embodiment of the present disclosure.

FIG. 7C illustrates the introducer of FIG. 7A retracted to deployfixation structures in accordance with an embodiment of the presentdisclosure.

FIG. 7D illustrates the introducer of FIG. 7A removed in accordance withan embodiment of the present disclosure.

FIG. 8A is an end view of a fixation assembly in accordance with anembodiment of the present disclosure.

FIG. 8B is an end view of a plurality of fixation assembliesrotationally offset in accordance with an embodiment of the presentdisclosure.

FIG. 8C is a sectional view of the therapy assembly of FIG. 7B with thefixation structures in a collapsed configuration in accordance with anembodiment of the present disclosure.

FIG. 8D is a longitudinal sectional view of the therapy assembly of FIG.7B.

FIGS. 9A and 9B are side and perspective views of a therapy deliveryelement with fixation structures in accordance with an embodiment of thepresent disclosure.

FIGS. 10A and 10B are side and perspective views of a therapy deliveryelement with free floating fixation structures in accordance with anembodiment of the present disclosure.

FIGS. 11A and 11B are side and perspective views of a therapy deliveryelement with trapezoidal fixation structures in accordance with anembodiment of the present disclosure.

FIGS. 12A and 12B are side and perspective views of a therapy deliveryelement with longitudinally spaced and rotationally offset fixationstructures on a single sleeve in accordance with an embodiment of thepresent disclosure.

FIGS. 13A and 13B are side and perspective views of a therapy deliveryelement with longitudinally spaced and rotationally offset trapezoidalfixation assemblies in accordance with an embodiment of the presentdisclosure.

FIGS. 14A and 14B are side and perspective views of a therapy deliveryelement with triangular fixation structures in accordance with anembodiment of the present disclosure.

FIG. 15 is a side view of a therapy delivery element with angledfixation surfaces in accordance with an embodiment of the presentdisclosure.

FIG. 16 is a side view of a therapy delivery element with hybridfixation surfaces in accordance with an embodiment of the presentdisclosure.

FIG. 17 illustrates a portion of a method of implanting a therapydelivery element in accordance with an embodiment of the presentdisclosure.

FIG. 18 illustrates a portion of a method of implanting a therapydelivery element in accordance with an embodiment of the presentdisclosure.

FIG. 19 is a flow chart of steps for implanting a therapy deliveryelement in accordance with an embodiment of the present disclosure.

The drawings are not necessarily to scale. Like numbers refer to likeparts or steps throughout the drawings.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The description that follows highlights spinal cord stimulation (SCS)system, the treatment of pelvic floor disorders, and peripheral nervefield stimulation (PNFS). However, it is to be understood that thedisclosure relates to any type of implantable therapy delivery systemwith one or more therapy delivery elements with one or more electrodesor sensors. For example, the present disclosure may be used as part of apacemaker, a defibrillator, a cochlear stimulator, a retinal stimulator,a stimulator configured to produce coordinated limb movement, a corticalstimulator, a deep brain stimulator, microstimulator, or in any otherneural stimulator configured to treat sleep apnea, shoulder sublaxation,headache, etc.

In another embodiment, one or more of the therapy delivery elements maybe a fluid or drug delivery conduit, such as a catheter, including aninner lumen that is placed to deliver a fluid, such as pharmaceuticalagents, insulin, pain relieving agents, gene therapy agents, or the likefrom a fluid delivery device (e.g., a fluid reservoir and/or pump) to arespective target tissue site in a patient.

In yet another embodiment, one or more of the therapy delivery elementsmay be a medical electrical lead including one or more sensingelectrodes to sense physiological parameters (e.g., blood pressure,temperature, cardiac activity, etc.) at a target tissue site within apatient. In the various embodiments contemplated by this disclosure,therapy may include stimulation therapy, sensing or monitoring of one ormore physiological parameters, fluid delivery, and the like. “Therapydelivery element” includes pacing or defibrillation leads, stimulationleads, sensing leads, fluid delivery conduit, and any combinationthereof. “Target tissue site” refers generally to the target site forimplantation of a therapy delivery element, regardless of the type oftherapy.

FIG. 1 illustrates a generalized therapy delivery system 10 that may beused in stimulation applications. The therapy delivery system 10generally includes an implantable pulse generator 12 (“IPG”), animplantable therapy delivery element 14, which carries an array ofelectrodes 18 (shown exaggerated for purposes of illustration), and anoptional implantable extension lead 16. The electrodes 18 are typicallyrings or hollow cylinders that extend around a portion of thecircumference of the therapy delivery element 14. Although only onetherapy delivery element 14 is shown, typically two or more therapydelivery elements 14 are used with the therapy delivery system 10.

The therapy delivery element 14 includes lead body 40 having a proximalend 36 and a distal end 44. The lead body 40 typically has a diameterranging between about 0.03 inches to about 0.07 inches and a lengthranging between about 30 cm to about 90 cm for spinal cord stimulationapplications. The lead body 40 may include a suitable electricallyinsulative coating, such as, a polymeric material (e.g., polyurethane orsilicone).

In the illustrated embodiment, proximal end 36 of the therapy deliveryelement 14 is electrically coupled to distal end 38 of the extensionlead 16 via a connector 20, typically associated with the extension lead16. Proximal end 42 of the extension lead 16 is electrically coupled tothe implantable pulse generator 12 via connector 22 associated withhousing 28. Alternatively, the proximal end 36 of the therapy deliveryelement 14 can be electrically coupled directly to the connector 22.

In the illustrated embodiment, the implantable pulse generator 12includes electronic subassembly 24 (shown schematically), which includescontrol and pulse generation circuitry (not shown) for deliveringelectrical stimulation energy to the electrodes 18 of the therapydelivery element 14 in a controlled manner, and a power supply, such asbattery 26.

The implantable pulse generator 12 provides a programmable stimulationsignal (e.g., in the form of electrical pulses or substantiallycontinuous-time signals) that is delivered to target stimulation sitesby electrodes 18. In applications with more than one therapy deliveryelement 14, the implantable pulse generator 12 may provide the same or adifferent signal to the electrodes 18.

Alternatively, the implantable pulse generator 12 can take the form ofan implantable receiver-stimulator in which the power source forpowering the implanted receiver, as well as control circuitry to commandthe receiver-stimulator, are contained in an external controllerinductively coupled to the receiver-stimulator via an electromagneticlink. In another embodiment, the implantable pulse generator 12 can takethe form of an external trial stimulator (ETS), which has similar pulsegeneration circuitry as an IPG, but differs in that it is anon-implantable device that is used on a trial basis after the therapydelivery element 14 has been implanted and prior to implantation of theIPG, to test the responsiveness of the stimulation that is to beprovided.

The housing 28 is composed of a biocompatible material, such as forexample titanium, and forms a hermetically sealed compartment containingthe electronic subassembly 24 and battery 26 protected from the bodytissue and fluids. The connector 22 is disposed in a portion of thehousing 28 that is, at least initially, not sealed. The connector 22carries a plurality of contacts that electrically couple with respectiveterminals at proximal ends of the therapy delivery element 14 orextension lead 16. Electrical conductors extend from the connector 22and connect to the electronic subassembly 24.

FIG. 2A illustrates the therapy delivery element 14 including one ormore electrical contacts 15 at the proximal end 36, and one or moreelectrodes 18 at the distal end 44. The contacts 15 and electrodes 18are electrically coupled via insulated wires running through the therapydelivery element 14. Proximal end 36 of the therapy delivery element 14is electrically and mechanically coupled to implantable pulse generator12 by the connector assembly 22. In the embodiment illustrated in FIGS.2A and 2B, the therapy delivery element 14 forms a medical electricallead.

The connector assembly 22 includes a plurality of discrete contacts 23located in the housing 28 that electrically couple contact rings 15 onthe proximal end of the therapy delivery element 14. The discretecontacts 23 are electrically coupled to circuitry 24 in the implantablepulse generator 12 by conductive members 21. Each contact ring 15 iselectrically coupled to one or more of the electrodes 18 located at thedistal end 44 of the therapy delivery element 14. Consequently, theimplantable pulse generator 12 can be configured to independentlydeliver electrical impulses to each of the electrodes 18.

Alternatively, the therapy delivery element 14 can be coupled to theimplantable pulse generator 12 through one or more lead extensions 16,as illustrated in FIG. 2B. The connector 20 at the distal end 38 of thelead extension 16 preferably includes a plurality of the contacts 23configured in a manner similar to the connector assembly 22.

FIG. 3 illustrates the therapy delivery element 14 used for spinal cordstimulation (SCS) implanted in the epidural space 30 of a patient inclose proximity to the dura, the outer layer that surrounds the spinalcord 32, to deliver the intended therapeutic effects of spinal cordelectrical stimulation. The target stimulation sites may be anywherealong the spinal cord 32, such as proximate the sacral nerves.

Because of the lack of space near the lead exit point 34 where thetherapy delivery element 14 exits the spinal column, the implantablepulse generator 12 is generally implanted in a surgically-made pocketeither in the abdomen or above the buttocks, such as illustrated in FIG.4. The implantable pulse generator 12 may, of course, also be implantedin other locations of the patient's body. Use of the extension lead 16facilitates locating the implantable pulse generator 12 away from thelead exit point 34. In some embodiments, the extension lead 16 serves asa lead adapter if the proximal end 36 of the therapy delivery element 14is not compatible with the connector 22 of the implantable pulsegenerator 12, since different manufacturers use different connectors atthe ends of their stimulation leads and are not always compatible withthe connector 22.

As illustrated in FIG. 4, the therapy delivery system 10 also mayinclude a clinician programmer 46 and a patient programmer 48. Clinicianprogrammer 46 may be a handheld computing device that permits aclinician to program neurostimulation therapy for patient using inputkeys and a display. For example, using clinician programmer 46, theclinician may specify neurostimulation parameters for use in delivery ofneurostimulation therapy. Clinician programmer 46 supports telemetry(e.g., radio frequency telemetry) with the implantable pulse generator12 to download neurostimulation parameters and, optionally, uploadoperational or physiological data stored by implantable pulse generator12. In this manner, the clinician may periodically interrogate theimplantable pulse generator 12 to evaluate efficacy and, if necessary,modify the stimulation parameters.

Similar to clinician programmer 46, patient programmer 48 may be ahandheld computing device. Patient programmer 48 may also include adisplay and input keys to allow patient to interact with patientprogrammer 48 and the implantable pulse generator 12. The patientprogrammer 48 provides patient with an interface for control ofneurostimulation therapy provided by the implantable pulse generator 12.For example, patient may use patient programmer 48 to start, stop oradjust neurostimulation therapy. In particular, patient programmer 48may permit patient to adjust stimulation parameters such as duration,amplitude, pulse width and pulse rate, within an adjustment rangespecified by the clinician via clinician programmer 46, or select from alibrary of stored stimulation therapy programs.

The implantable pulse generator 12, clinician programmer 46, and patientprogrammer 48 may communicate via cables or a wireless communication.Clinician programmer 46 and patient programmer 48 may, for example,communicate via wireless communication with the implantable pulsegenerator 12 using RF telemetry techniques known in the art. Clinicianprogrammer 46 and patient programmer 48 also may communicate with eachother using any of a variety of local wireless communication techniques,such as RF communication according to the 802.11 or Bluetoothspecification sets, infrared communication, e.g., according to the IrDAstandard, or other standard or proprietary telemetry protocols.

Since the implantable pulse generator 12 is located remotely from targetlocation 50 for therapy, the therapy delivery element 14 and/or theextension lead 16 is typically routed through a pathway 52subcutaneously formed along the torso of the patient to a subcutaneouspocket 54 where the implantable pulse generator 12 is located. As usedhereinafter, “lead” and “lead extension” may be used interchangeably,unless context indicates otherwise.

The therapy delivery elements 14 are typically fixed in place near thelocation selected by the clinician using the present suture anchors 60.The suture anchors 60 can be positioned on the therapy delivery element14 in a wide variety of locations and orientations to accommodateindividual anatomical differences and the preferences of the clinician.The suture anchors 60 may then be affixed to tissue using fasteners,such as for example, one or more sutures, staples, screws, or otherfixation devices. The tissue to which the suture anchors 60 are affixedmay include subcutaneous fascia layer, bone, or some other type oftissue. Securing the suture anchors 60 to tissue in this manner preventsor reduces the chance that the therapy delivery element 14 will becomedislodged or will migrate in an undesired manner.

FIG. 5 illustrates the therapy delivery element 14 used for pelvic floordisorders such as, urinary incontinence, urinary urge/frequency, urinaryretention, pelvic pain, bowel dysfunction (constipation, diarrhea),erectile dysfunction, are bodily functions influenced by the sacralnerves. The organs involved in bladder, bowel, and sexual functionreceive much of their control via the second, third, and fourth sacralnerves, commonly referred to as S2, S3 and S4 respectively. Electricalstimulation of these various nerves has been found to offer some controlover these functions. Several techniques of electrical stimulation maybe used, including stimulation of nerve bundles 72 within the sacrum 70.The sacrum 70, generally speaking, is a large, triangular bone situatedat the lower part of the vertebral column, and at the upper and backpart of the pelvic cavity. The spinal canal 74 runs throughout thegreater part of the sacrum 70. The sacrum is perforated by the posteriorsacral foramina 76 and anterior sacral foramina 78 that the sacralnerves 72 pass through.

Specifically, urinary incontinence is the involuntary control over thebladder that is exhibited in various patients. The therapy deliveryelement 14 is percutaneously implanted through the foramina 76, 78 ofthe sacral segment S3 for purposes of selectively stimulating the S3sacral nerve 72. Stimulation energy is applied through the lead 14 tothe electrodes 18 to test the nerve response. The electrodes 18 aremoved back and forth to locate the most efficacious location, and thelead 14 is then secured by suturing the lead body to subcutaneous tissueposterior to the sacrum 70 and attached to the output of aneurostimulator IPG 12.

FIG. 6 illustrates the therapy delivery element 14 used for deliveringperipheral nerve field stimulation (PNFS) to a patient. Therapy deliveryelement 14 delivers PNFS from the implantable pulse generator 12 to thetissue of patient at target location 50A where patient experiences pain.Clinician programmer 46 and patient programmer 48 may communicate viawireless communication with the implantable pulse generator 12.

Therapy delivery element 14 may be implanted within or between, forexample, intra-dermal, deep dermal, or subcutaneous tissue of patient atthe location 50A where patient experiences pain. Subcutaneous tissueincludes skin and associated nerves, and muscles and associated nervesor muscle fibers. In the illustrated example, location 50A is a regionof the lower back. In other examples, the therapy delivery element 14may extend from implantable pulse generator 12 to any localized area ordermatome in which patient experiences pain, such as various regions ofthe back, the back of the head, above the eyebrow, and either over theeye or under the eye, and may be used to treat failed back surgerysyndrome (FBBS), cervical pain (e.g., shoulder and neck pain), facialpain, headaches supra-orbital pain, inguinal and pelvic pain, chest andintercostal pain, mixed pain (e.g., nociceptive and neuropathic),visceral pain, neuralgia, peroneal pain, phantom limb pain, andarthritis.

FIGS. 7A and 7B illustrate a therapy assembly 100 including a therapydelivery element 102 located in lumen 105 (see FIG. 8C) of introducer104 in accordance with an embodiment of the present disclosure. Thetherapy delivery element 102 includes a plurality of ring electrodes 106near distal end 108. The ring electrodes 106 wrap around the peripheryof the distal end 108 so the radial orientation of the therapy deliveryelement 102 does not impact its ability to simulate the target nervetissue during testing and implantation.

In use, the surgeon positions the therapy assembly 100 illustrated inFIG. 7B adjacent to the target nerve tissue using known techniques (seee.g., FIGS. 15 and 16). The energized electrodes 106 stimulate theadjacent nerve tissue in order to map the nerve response and betterposition the therapy delivery element 102.

As illustrated in FIGS. 7C and 7D, once the mapping process is completedand the surgeon is satisfied with placement of the therapy deliveryelement 102, the introducer 104 is withdrawn to release fixationstructures 110A, 110B, 110C, 110A′, 110B′, 110C′, 110A″, 110B″, 110C″(“110”), from one or more fixation assemblies 112A, 112B, 112C (“112”).Each of the fixation structures 110 expands radially outward fromcentral axis 118 to a deployed configuration 114. The fixationassemblies 112 are longitudinally spaced along the therapy deliveryelement 102. The axial spacing 113 between each fixation assembly 112can be the same or different.

In the illustrate embodiment, the fixation structures 110 are generallyplanar structures with major surfaces 116 that are parallel to, andextend generally radially out from, central axis 118 of the therapydelivery element 102. The axial orientation of the fixation structures110 when in the deployed configuration 114 facilitates subsequentremoval of the therapy delivery element 102.

Each fixation structure 112 includes a proximal edge surface 120 thatresists displacement of the therapy delivery element 102 along thecentral axis 118 in a proximal direction 122, and a distal edge surface124 that resists displacement in a distal direction 126. Friction of themajor surfaces 116 also resists displacement in both directions 122, 126along the central axis 118.

The total surface area of the proximal edge surfaces 120 is preferablywithin about +/−20% or less than the total surface area of the distaledge surfaces 124, so that the fixation structures 110 provide generallysymmetrical fixation of the therapy delivery element 102 in a livingbody. As used herein. “generally symmetrical resistance to displacement”refers to resistance to a displacement force applied to a therapydelivery element in a proximal direction along a central axis that iswithin about +/−20% or less to a resistance to a displacement forceapplied in the distal direction along the central axis.

The fixation structures 112 are preferably attached to sleeve 130, whichis subsequently bonded to the therapy delivery element 102. As usedherein “bonded” or “bonding” refers to adhesive bonding, solventbonding, ultrasonic welding, thermal bonding, and a variety of othertechniques. In another embodiment, the fixation structures 112 arediscrete elements that are bonded directly to the therapy deliveryelement 102.

The fixation structures 112 are can be made from a variety ofbio-compatible polymeric or metal materials, such as for example,polyethylene terephthalate (PET), Nylon, polyether ether ketone (PEEK),polyproylene, high-performance polyethylenes, bioabsorbale polymers,such as polyglutamic acid (PGA), poly-L-lactide (PLLA), orpolycaprolactone (PCL), urethanes such as Tecothane, silicone, Nitinol,stainless steel, MP35N, titanium, or any combination of these materials.Tecothane® aromatic polyether-based thermoplastic polyurethanes areresins which exhibit solvent resistance and biostability over a widerange of hardness. The introducer 104 are can be made from a variety offlexible bio-compatible polymeric or metal materials, such as forexample, polyethylene terephthalate (PET). Nylon, polyproylene,high-performance polyethylenes, urethane, silicone, or any combinationof these materials.

As best illustrated in FIG. 7D, the fixation assemblies 112 can be bothrotationally and axially offset from each other. For example, thefixation assembly 112B is rotated about 60 degrees relative to thefixation assemblies 112A, 112C. Edge surfaces 120, 124 of the fixationstructures 110A, 110B, 110C, 110A″, 110B″, 110C″ on the fixationassemblies 112A, 112C are rotationally offset from the edge surfaces120, 124 on the fixation structures 110A′, 110B′, 110C on the fixationassembly 112B. The major surfaces 116 and the edge surfaces 120, 124 ofthe fixation structures 110A and 110A″ on the fixation assemblies 110A,110C are generally in the same plane. The same is also true for thefixation structures 110B and 110B″ and the fixation structures 110C and110C″.

The edge surfaces 120, 124 and major surfaces 116 of the fixationstructure 110A′ on the fixation assembly 112B, however, are not in thesame plane (i.e., out-of-plane) with the corresponding fixationstructures 110A, and 110A″ on the fixation assemblies 112A, 112C.Consequently, the fixation structures 112 provide nine proximal edgesurfaces 120 that resist displacement in direction 122 and nine distaledge surfaces 124 that resist displacement in direction 126.

FIG. 8A is an axial view from either end of the fixation assembly 112Aillustrated in FIGS. 7C and 7D. Each of the fixation structures 110includes a radial dimension 136, axial dimension 137 (see FIG. 7C), andthickness 138. The radial dimension 136 and the thickness 138 definesurface area 146 of the edge surfaces 120. Since the fixation structures110 are symmetrical, the distal edge surfaces 124 have the same surfacearea 146.

FIG. 8B is an axial view of the fixation assemblies 112A, 112B asconfigured in FIG. 7D, with fixation assembly 112B rotationally offsetat angle 140 from the fixation assembly 112A. In the illustratedembodiment the angle 140 is about 60 degrees, although the actual anglecan vary. This configuration doubles the number of edge surfaces 120,124 resisting displacement in directions 122, 126, respectively.

In the illustrated embodiment, the edge surfaces 120, 124 areperpendicular to the central axis 118 and have about the same surfacearea. The fixation structures 110 are generally symmetrical. As aresult, the fixation structures 110 provide generally symmetricalresistance to displacement of the therapy delivery element 102 in eitherthe proximal direction 124 or the distal direction 126. The presentfixation structure 110 provides bi-directional axial fixation usingopposite edge surfaces of a single structure.

The fixation structures 110 and the sleeve 130 are preferably extrudedand then cut to length. The fixation structures 110 are optionallyconstructed from a radiopaque filled material. Any number of fixationstructures 110 can be used, but typically there are about 2 to about 12.Any number of fixation assemblies 112 can be used, but typically thereare about 2 to about 5.

The sleeve 130 typically has an inside diameter 131 corresponding tooutside diameter of the therapy delivery element 102. The sleeve 130 hasa thickness 148 in a range between about 0.005 inches to about 0.015inches, or about 0.008 inches. The fixation structures 110 can have aradial dimension 136 in a range between about 0.050 inches to about0.100 inches. Axial dimensions 137 are typically in a range of betweenabout 0.030 inches to about 0.500 inches. The axial spacing 113 betweenadjacent fixation assemblies 110 is typically in a range of betweenabout 0.050 inches to about 0.200 inches.

In some preferred embodiments, three discrete fixation assemblies 112 asdisclosed in FIG. 7D with three fixation structures 110 arranged at 120degree intervals were bonded to a therapy delivery element 102. Themiddle of the three fixation assemblies 112 was rotationally offset by60 degrees. The fixation assemblies 112 were constructed fromTecothane®. Each fixation structure 110 had a thickness of about 0.008inches, a radial dimension 136 of about 0.055 inches, and an axialdimension 137 in a range of about 0.070 inches to about 0.200 inches.The resulting edge surfaces 120, 124 have an area of about 0.0004square-inches. The axial spacing was in a range of between about 0.110inches to about 0.135 inches. The resulting therapy delivery elements102 exhibited a pull-out force 132 from tissue in a range of betweenabout 0.920 pounds to about 2.160 pounds.

The general symmetry of the present fixation structures simplifiesmodification to alter the pull-out force for a particular application.The pull-out force can be increased or decreased by adjusting the radialdimension, axial dimension, the number of fixation structures, or acombination thereof. A therapy delivery element with the presentfixation structures preferably exhibit a pullout-force from the livingbody in a range of between about 0.50 pounds to about 3.00 pounds.

FIG. 7D illustrates the therapy delivery element 102 with the introducer104 fully withdrawn. Tension force 132 can be applied to proximal end134 to remove the therapy delivery element 102 from the patient. As thetherapy delivery element 102 is displaced in removal direction 122, edgesurfaces 120 of the fixation elements 110 either cut through thesurrounding tissue, fold inward toward the therapy delivery element 102,or a combination thereof. The edge surfaces 120 typically have a surfacearea of engagement with the tissue of about the radial dimension 120times the thickness of the fixation structures 110.

FIG. 8C is a sectional view of the therapy assembly 100 of FIG. 7B. Thefixation assembly 112A is retained within the introducer 104 incollapsed configuration 142 in accordance with an embodiment of thepresent disclosure. The fixation structures 110A, 110B, 110C collapseradially inward and wrap circumferentially around the therapy deliveryelement 102 and/or sleeve 130 as the therapy delivery element 102 isinserted into the lumen of the introducer 104. In the preferredembodiment, the surgeon rotates the therapy delivery element 102 as itis being inserted into the lumen 105 of the introducer 104 in order tofacilitate the fixation structures 110 wrapping circumferentially asshown in FIG. 8C.

The fixation structures 110A, 110B, 110C preferably follow the contourof the sleeve 130 (or the therapy delivery element 102 when no sleeve130 is used), but preferably do not overlap in order to minimize thediameter of the therapy assembly 100. Overlapping can be avoided byadjusting the number of fixation structures 110 and the radial dimension120 of the fixation structures 110.

FIG. 8D is a section side view of the therapy assembly 100 of FIG. 8Awith the fixation assemblies 112A, 112B, 112C in the collapsedconfiguration 142. The fixation structures 112 wrap around the sleeve130 as discussed above.

FIGS. 9A and 9B illustrate axially oriented fixation structures 150A,150B, 150C (“150”) attached to a therapy delivery element 152 inaccordance with an embodiment of the present disclosure. Major surfaces154 on the fixation structures 150 are generally parallel tolongitudinal axis 156 of the therapy delivery element 152. The fixationstructures 150 optionally include holes 158 to promote tissue in-growth.Promoting tissue in-growth increases the force 132 required to removethe therapy delivery element 152 from the patient.

Proximal edge surfaces 160 and distal edge surfaces 162 are generallyperpendicular to the central axis 156 and have about the same surfacearea. The fixation structures 150 are generally symmetrical so that eachproximal edge surface 160 has an opposing distal edge surface 162 withabout the same surface area. As a result, the fixation structures 150provide generally symmetrical resistance to displacement of the therapydelivery element 152 in either proximal direction 164 or the distaldirection 166 along the central axis 156. The present fixationstructures 110 provide bi-directional axial fixation using opposite edge160, 162 surfaces of a single structure.

FIGS. 10A and 10B illustrate alternate axially oriented fixationstructures 170A, 170B. 170C (“170”) attached to a therapy deliveryelement 172 in accordance with an embodiment of the present disclosure.Portion 174 of the sleeve 176 is removed so that proximal ends 178 ofthe fixation structures 170 are not attached to the therapy deliveryelement 172. The proximal ends 178 are free to shift with proximal end180 of the therapy delivery element 172, such as during active movementby the patient. The free-floating proximal ends 178 act as strain relieffor the fixation structures 170, reducing the risk of displacing thetherapy delivery element 172.

Edge surfaces 182, 184 are generally perpendicular to the central axis186 and have about the same surface area. The proximal ends 178,however, also tend to fold toward the major surfaces of the fixationstructures 170 in direction 188 during removal of the therapy deliveryelement 172 in direction 190, facilitating release of any adheredtissue. When the proximal ends 178 are folded in direction 190, thefolded structures 178 approximate the edge surfaces 184 sufficiently toprovide generally symmetrical resistance to displacement in eitherdirection along the central axis 186.

FIGS. 11A and 11B illustrate alternate axially oriented fixationstructures 200A, 200B, 200C (“200”) with tapered edge surfaces 202, 204in accordance with an embodiment of the present disclosure. The taperededge surfaces 202, 204 are oriented at angles 206, 208 with respect tocentral axis 210, respectively. In the illustrated embodiment, thetapered edge surfaces 202, 204 are generally symmetrical, resulting in agenerally symmetrical resistance to displacement in either directionalong the central axis 210.

In an alternate embodiment, the angles 206, 208 are different and thetapered edge surfaces 202, 204 have different surface areas. Viewedalong the central axis 210, however, the effective edge surfaces 202,204 acting along the central axis 210 are sufficiently similar that theresistance to displacement is about the same in either direction alongthe central axis 210. As used herein. “effective surface area” refers toa surface area of a fixation structure measured in a plane perpendicularto a central axis of a therapy delivery element.

The fixation structures 200 can be attached to a single sleeve or tomultiple discrete sleeves 212A, 212B (“212”). Where discrete sleeves 212are used, the resulting discrete fixation assembly 214A, 214B can beradially and/or axially offset from one another.

FIGS. 12A and 12B illustrate multiple groups of fixation structures220A, 220B (“220”). 222A, 222B (“222”), 224A, 224B (“224”) attached to asingle sleeve 226 in accordance with an embodiment of the presentdisclosure. The fixation structures 222A, 222B are rotated 90 degreesrelative to the fixation structures 220A, 220B, 224A, 224B. The groupsof fixation structures 222, 224, 226 are separated by axially spacing228.

The configuration of the present embodiment increases the number of edgesurfaces 230, 232 engaged with the patient's tissue at the implantationsite, enhancing bidirectional fixation along central axis 238 of thetherapy delivery element 236. At the same time the size of each majorsurface 234 and the total surface area of the major surfaces 234 areboth reduced, with a corresponding decrease in tissue adhesion. For someembodiments, increasing the number of edge surfaces 230, 232, whilereducing the total surface area of the major surfaces 234 on thefixation structures 222, 224, 226 is the optimum balance of fixationwhile minimizing tissue adhesion.

FIGS. 13A and 13B illustrate multiple discrete axially oriented fixationassemblies 240A, 240B, 240C (“240”) each with a plurality of taperedfixation structures 242 in accordance with an embodiment of the presentdisclosure. Tapered edge surfaces 244, 246 operate as discussed herein.As best illustrated in FIG. 13B, the discrete fixation assemblies 240permit rotational positioning around central axis 248 to be offset,increasing the number of active edge surfaces 244, 246 interacting withthe tissue.

FIGS. 14A and 14B illustrate multiple discrete fixation assemblies 250A,250B, 250C (“250”) with no axial spacing and pointed fixation structures252 in accordance with an embodiment of the present disclosure. Theproximal and distal edge surfaces 254, 256 are tapered with respect tocentral axis 258 of the therapy delivery element 260. The tapered edgesurfaces 254, 256 operate to reduce the required removal force 132,while providing generally symmetrical resistance to displacement ineither direction along the central axis 258, as discussed herein.

FIG. 15 is a side view of a therapy delivery element 262 with fixationassembly 264 having edge surfaces 266A, 266B (“266”) that angle inwardto create undercuts 268 in accordance with an embodiment of the presentdisclosure. The proximal edge surfaces 266A are generally equivalent tothe distal edge surfaces 266B in terms of surface area and shape,resulting in generally symmetrical fixation of the therapy deliveryelement 262 along central axis 270, while the undercuts 268 provideenhanced fixation.

FIG. 16 is a side view of a therapy delivery element 280 with hybridedge surfaces 282A, 282B (“282”) and 284A, 284B (“284”) in accordancewith an embodiment of the present disclosure. Edges 282 provideundercuts 286, while edges 284 are generally perpendicular to centralaxis 288.

Due to the undercuts 286, the opposing edge surfaces 282A and 284B havedifferent surface areas, as do opposing edge surfaces 284A and 282B. Thesum of the proximal edge surfaces 282A, 284A, however, are generallyequivalent to the sum of the distal edge surfaces 282B, 284B in terms ofsurface area and shape, resulting in generally symmetrical fixation ofthe therapy delivery element 280 along central axis 288.

FIG. 17 illustrates one embodiment of implanting a therapy deliveryelement 300 through introducer 302 in sacral nerve in accordance with anembodiment of the present disclosure. In one embodiment, therapydelivery element 300 is advanced percutaneously at a selected anglethrough the introducer 302 disposed at the selected foramen 304. Thetherapy delivery element 300 may be inserted near any of the sacralnerves including the S1, S2, S3, or S4, sacral nerves accessed via thecorresponding foramen depending on the necessary or desired physiologicresponse. Stylet 306 is optionally located in the therapy deliveryelement 300 to increase stiffness and column strength.

In one embodiment, the introducer 302 is advanced in direction 308 overa guide wire previously percutaneously advanced from the skin incisioninto the foramen to establish the angle of advancement. In yet anotherembodiment, a multi-part introducer can be employed having an innerintroducer element that may be first advanced to the site by itself orover a previously introduced guide wire, and an outer introducer can beintroduced over the inner element to dilate the tissue, whereupon theinner element is removed. Any percutaneous introduction tools andtechniques may be employed that ultimately result in the therapydelivery element 300 at the location of FIG. 17.

As illustrated in FIG. 18, once nerve mapping is completed and thetherapy delivery element 300 is in the desired location, the introducer302 is retracted proximally in direction 310. The fixation structures312 are released from the introducer 302 and engage with surroundingsubcutaneous tissue 314 to secure the electrodes 316 relative to theforeman 310. In the illustrated embodiment, the fixation structures 312are axially offset to increase the chance that at least one fixationstructure 312 will engage with the muscle tissue located along rearsurface of the sacrum 318. In one embodiment the fixation structures 312can be seen under fluoroscopy to allow the physician to verify that thefixation structures 312 are deployed.

FIG. 19 is a flow chart outlining one method of implanting a therapyassembly in a living body. The method includes inserting an introduceradjacent into the living body with a distal end adjacent to animplantation site (350). A distal end of a therapy delivery element isthen inserted into a lumen in the introducer to collapse radially inwardfixation structures attached to the therapy delivery element near thedistal end (352). The therapy delivery element is rotated slightlyduring insertion into the introducer to wrap the fixation structurescircumferentially around the therapy delivery element to a collapsedconfiguration (354). Placement of the therapy delivery element in theliving body is confirmed (356). The introducer is retracted from theliving body to deploy the fixation structures to a deployedconfiguration (358). The fixation structures include major surfacesgenerally parallel with, and extending radially outward from a centralaxis of the therapy delivery element, a proximal edge surface orientedtoward the proximal end of the therapy delivery element, and a distaledge surface oriented toward the distal end of the therapy deliveryelement. Electrical contacts at a proximal end of the therapy deliveryelement are electrically coupled to an implantable pulse generator(360). The proximal and distal edge surfaces of the fixation structuresare engaged with tissue in the living body to provide generallysymmetrical resistance to displacement of the therapy delivery elementwithin the living body in either direction along the central axis (362).

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range is encompassed within this disclosure. The upper and lowerlimits of these smaller ranges which may independently be included inthe smaller ranges is also encompassed within the disclosure, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either bothof those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the various methods and materials arenow described. All patents and publications mentioned herein, includingthose cited in the Background of the application, are herebyincorporated by reference to disclose and described the methods and/ormaterials in connection with which the publications are cited.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present disclosure isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

Other embodiments are possible. Although the description above containsmuch specificity, these should not be construed as limiting the scope ofthe disclosure, but as merely providing illustrations of some of thepresently preferred embodiments. It is also contemplated that variouscombinations or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of thisdisclosure. It should be understood that various features and aspects ofthe disclosed embodiments can be combined with or substituted for oneanother in order to form varying modes disclosed. Thus, it is intendedthat the scope of at least some of the present disclosure should not belimited by the particular disclosed embodiments described above.

Thus the scope of this disclosure should be determined by the appendedclaims and their legal equivalents. Therefore, it will be appreciatedthat the scope of the present disclosure fully encompasses otherembodiments which may become obvious to those skilled in the art, andthat the scope of the present disclosure is accordingly to be limited bynothing other than the appended claims, in which reference to an elementin the singular is not intended to mean “one and only one” unlessexplicitly so stated, but rather “one or more.” All structural,chemical, and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the present disclosure, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims.

What is claimed is:
 1. An apparatus, comprising: a therapy delivery element having a body that extends along a central axis, wherein the body includes a distal end and a proximal end opposite the distal end; one or more electrodes located on the therapy delivery element; a first fixation assembly that is coupled to the therapy delivery element, wherein the first fixation assembly includes a plurality of first fixation structures that, in a deployed configuration, each protrude radially outward from the body of the therapy delivery element; and a second fixation assembly that is coupled to the therapy delivery element, wherein the second fixation assembly includes a plurality of second fixation structures that, in the deployed configuration, each protrude radially outward from the body of the therapy delivery element, and wherein the first fixation structures are rotationally offset with respect to the second fixation structures in the deployed configuration; wherein: at least one of the first fixation structures or at least one of the second fixation structures includes an edge surface that angles inward so as to create an undercut; and for the at least one of the first fixation structures or the at least one of the second fixation structures that includes the edge surface that angles inward, an opposing edge surface extends perpendicularly to the central axis.
 2. The apparatus of claim 1, further comprising a sleeve, wherein the first fixation assembly and the second fixation assembly are attached to the sleeve, and wherein the sleeve is bonded to the therapy delivery element.
 3. The apparatus of claim 1, wherein the first fixation structures and the second fixation structures are each radially collapsible in a collapsed configuration.
 4. The apparatus of claim 3, wherein in the collapsed configuration: the first fixation structures each wrap around the body of the therapy delivery element but do not overlap with one another; and the second fixation structures each wrap around the body of the therapy delivery element but do not overlap with one another.
 5. The apparatus of claim 4, wherein the first fixation structures and the second fixation structures each resist displacement of the therapy delivery element in a distal direction or in a proximal direction along the central axis.
 6. The apparatus of claim 1, wherein at least one of the first fixation structures or at least one of the second fixation structures includes one or more holes therein.
 7. The apparatus of claim 1, wherein at least one of the first fixation structures or at least one of the second fixation structures has a free-floating end that is unattached to the therapy delivery element.
 8. The apparatus of claim 1, wherein the first fixation structures and the second fixation structures each have a rectangular shape.
 9. The apparatus of claim 1, wherein at least one of the first fixation structures or at least one of the second fixation structures includes tapered edges.
 10. The apparatus of claim 9, wherein at least one of the tapered edges includes a segment that extends in parallel with the central axis.
 11. The apparatus of claim 1, wherein no axial spacing exists between the first fixation assembly and the second fixation assembly.
 12. An apparatus, comprising: a therapy delivery element having a body that extends along a central axis, wherein the body includes a distal end and a proximal end opposite the distal end; one or more electrodes located on the therapy delivery element; and at least a first fixation assembly and a second fixation assembly each coupled to the therapy delivery element, wherein the first fixation assembly and the second fixation assembly are spaced apart in a longitudinal direction along the central axis, and wherein the first fixation assembly includes a plurality of first fixation structures, and wherein the second fixation assembly includes a plurality of second fixation structures; at least one of the first fixation structures or at least one of the second fixation structures includes an edge surface that angles inward so as to create an undercut; for the at least one of the first fixation structures or the at least one of the second fixation structures that includes the edge surface that angles inward, an opposing edge surface extends perpendicularly to the central axis; wherein: in a collapsed configuration, each of the first fixation structures and second fixation structures radially wraps around the body of the therapy delivery element; in a deployed configuration, each of the first fixation structures and second fixation structures protrudes radially outward with respect to the central axis and perpendicularly with respect to a surface of the therapy delivery element in a side view; and in the deployed configuration, each of the first fixation structures and second fixation structures points in a different radial direction.
 13. The apparatus of claim 12, wherein for each of the first and second fixation assemblies in the collapsed configuration: none of the first and second fixation structures overlap with one another.
 14. The apparatus of claim 12, wherein in the deployed configuration, the first and second fixation structures each resist displacement of the therapy delivery element in a distal direction or in a proximal direction along the central axis.
 15. The apparatus of claim 12, wherein at least one of first and second fixation structures includes a plurality of openings therein.
 16. The apparatus of claim 12, wherein no intermediate elements exist between the first and second fixation assemblies along the central axis.
 17. The apparatus of claim 12, further comprising a sleeve, wherein the first fixation assembly and the second fixation assembly are attached to the sleeve, and wherein the sleeve is bonded to the therapy delivery element.
 18. An apparatus for delivering electrical stimulation to a patient, comprising: a therapy delivery element having a body that extends along a central axis, wherein the body includes a distal end and a proximal end opposite the distal end; one or more electrodes located on the therapy delivery element; a first fixation assembly that is coupled to the therapy delivery element, wherein the first fixation assembly includes a plurality of first fixation structures that, in a deployed configuration, each protrude radially outward from the body of the therapy delivery element; a second fixation assembly that is coupled to the therapy delivery element, wherein the second fixation assembly includes a plurality of second fixation structures that, in the deployed configuration, each protrude radially outward from the body of the therapy delivery element, and wherein the first fixation structures are rotationally offset with respect to the second fixation structures in the deployed configuration; and a sleeve, wherein the first fixation assembly and the second fixation assembly are attached to the sleeve, and wherein the sleeve is bonded to the therapy delivery element; wherein: the first fixation structures and the second fixation structures are each radially collapsible in a collapsed configuration under which: the first fixation structures each wrap around the body of the therapy delivery element but do not overlap with one another, and the second fixation structures each wrap around the body of the therapy delivery element but do not overlap with one another, and wherein none of the first or second fixation structures circumferentially overlap when wrapped around the body of the therapy delivery element; and the first fixation structures and the second fixation structures each resist displacement of the therapy delivery element in a distal direction or in a proximal direction along the central axis.
 19. The apparatus of claim 18, further comprising a third fixation assembly that is coupled to the therapy delivery element, wherein the third fixation assembly includes a plurality of third fixation structures that: in the deployed configuration, each protrude radially outward from the body of the therapy delivery element; and in the collapsed configuration, each wrap around the body of the therapy delivery element; wherein in the deployed configuration, the third fixation structures are rotationally offset with respect to the second fixation structures but are rotationally aligned with respect to the first fixation structures.
 20. The apparatus of claim 18, wherein in the deployed configuration, at least some of the first fixation structures and the second fixation structures protrude perpendicularly with respect to a surface of the therapy delivery element in a side view. 